feat: add path relationship methods (relativeTo, commonStart, commonEnd)

[shaungrady]

Add three new methods for analyzing path relationships:

• relativeTo(base): Extract relative path from a base path

  • Returns the segments needed to concat to base to get the full path
  • Returns null if path doesn't start with base
  • Inverse operation of concat()

• commonStart(other): Find common prefix between two paths

  • Returns longest shared starting sequence
  • Returns empty path if no common prefix

• commonEnd(other): Find common suffix between two paths

  • Returns longest shared ending sequence
  • Returns empty path if no common suffix

All methods:

• Support wildcards and indices mode options
• Propagate instance configuration
• Include comprehensive test coverage (60 tests)
• Include JSDoc documentation with examples
• Added to README with usage examples

These methods enable powerful workflows like path decomposition,
finding shared parent paths, and extracting relative paths for display.